2025 Safe Yield Reevaluation

Background

The Safe Yield of the Chino Basin is the long-term average annual quantity of groundwater that can be produced from the Basin without causing an undesirable result. Calculating the Safe Yield is necessary for Watermaster to fulfill much of its obligations.

The Judgment set the initial Safe Yield at 140,000 acre-feet per year (afy). The Safe Yield has been recalculated and reset twice since the original adjudication in 1978: once for the period of 2011 through 2020, and once for the period of 2021 through 2030. The current Safe Yield is 131,000 afy, which resulted from the 2020 Safe Yield Recalculation (2020 SYR).

The two Safe Yield recalculations were completed pursuant to a methodology developed in 2015 (2015 SYRM) and includes the use of the Chino Basin Watermaster’s (Watermaster’s) groundwater-flow model to calculate the projected annual net recharge in the Chino Basin. The 2015 Safe Yield Reset Methodology was approved by a Court order in April 2017 (2017 Court Order).

The 2017 Court Order included other stipulations such as (1) approving the reset of the Safe Yield for 2011 through 2020, (2) mandating that the Safe Yield be recalculated and reset for the period of 2021 through 2030, (3) allowing for the update of the 2015 SY Reset methodology, and (4) requiring that the groundwaterflow model (called the Chino Valley Model, or CVM) be updated and that the Safe Yield (for 2021 through 2030) be reevaluated by June 2025. This mandate for reevaluating the Safe Yield is known as the 2025 Safe Yield Reevaluation (2025 SYR).

In 2021 and 2022, Watermaster developed an updated Safe Yield reset methodology with the advice and assistance from the parties and their technical consultants. This methodology, known as the 2022 SYRM, addressed many of the comments on the 2020 SYR and better accounts for the inherent uncertainty in groundwater-flow model parameters, future hydrology, and future cultural conditions (e.g., groundwater pumping, land use, irrigation patterns). The 2022 SYRM was approved by the Court in December 2022 and must be used for the 2025 SYR.

SCOPE OF THE 2025 SYR

The 2025 SYR was initiated in spring 2023. The scope of the 2025 SYR follows the 2022 SYRM and comprises the following tasks:

1. Update the groundwater-flow model that was used in the 2020 Safe Yield Recalculation

2. Generate multiple calibrated realizations based on the updated model

3. Develop projection realizations that include the range of future scenarios of hydrology and cultural conditions in the Chino Basin

4. Simulate projection realizations

5. Evaluate simulation results and calculate Safe Yield

6. Develop 2025 SYR report

7. Reset Safe Yield (if necessary)

If the results of Task 5 indicate that the Safe Yield for the period of 2021 through 2030 is different than the current Safe Yield by more than 2.5 percent, Watermaster will seek the advice and recommendation of the Pool and Advisory Committees before making a recommendation to the Court regarding potential changes to the Safe Yield.

CURRENT SAFE YIELD

131,000

ACRE-FEET PER YEAR (AFY)

Status As Of October 2023

As of October 2023, Watermaster is completing Task 1 and has initiated Tasks 2 and 3. On August 30, 2023, Watermaster conducted its first workshop for the 2025 SYR to discuss the proposed updates to the CVM (Task 1). The proposed updates to the model include incorporating new information gathered from new wells that have been constructed since the development of the prior CVM. More detail can be found in the presentation materials from the August workshop here

To support the development of the projection scenarios that will be used in the 2025 SYR, Watermaster is hosting a workshop for the parties and other stakeholders on October 24, 2023. The objectives of this workshop are to ensure parties’ collective understanding of the scenario design process and gather input from the parties and stakeholders on the drivers of changes in water demands and supply plans. Input from this workshop will inform the scenarios that will be developed for the 2025 SYR.

Future Schedule

The graphic shows the future meetings and workshops that will support the 2025 SYR, including the date and subject. You can also view the schedule here

DID YOU KNOW: The 2000 OBMP Implementation Plan requires that the Safe Yield of the Chino Basin be recalculated every 10 years, beginning in 2011.